Arc furnace process for the production of titanium carbide



J. J. SCOTT 3,161,472 FOR THE PRODUCTION OF TITANIUM CARBIDE Dec. 15,1964 ARC FURNACE PROCESS 5 Sheets-Sheet 1 Filed Feb. 25, 1958 INVENTORJ: ScoTT JOHN BY ATTORNEY Dec. 15, 1964 J. J. scoTT 3,161,472

ARC FURNACE PROCESS FOR THE PRODUCTION OF TITANIUM CARBIDE Filed Feb.25, 1958 5 Sheets-Sheet 2 INVENTOR JOHN J ScoTT BY 4ni7-mnm A 7' TOENEYJ. J. SCOTT Dec. 15, 1964 ARC FURNACE PROCESS FOR THE PRODUCTION OFTITANIUM CARBIDE 5 Sheets-Sheet 3 Filed Feb. 25, 1958 INVENTOR JOHN JScorr Arro Y Dec. 15, 1964 ARC FURNACE PROCESS FOR THE PRODUCTION OFTITANIUM CARBIDE Filed Feb. 25, 1958 FURNACE CUREEN T J. J. scoTT3,161,472

5 Sheets-Sheet 4 Fo/e FUENACE DESCEIBED. 551.5: 7' OPEzA TING CONDITIONSONLY FzoM WITHIN 771/5 AREA.

fine/VA CE VOL. 771 $5 INVENTOR JDHN .1. 55471-7 7": ATTOR Y 1964 J. J.SCOTT 3, 6 72 ARC FURNACE PROCESS FOR THE PRODUCTION OF TITANIUM CARBIDEFiled Feb. 25, 1958 5 Sheets-Sheet 5 INVENTOR L/a/rz 1/. 5601! BY f%w%.M4

ATTORNEY United States Patent Ofitice 3,161,472 ARC FURNACE PROCESS FORTHE PRODUCTION F TITANIUM CARBIDE John J. Scott, Wilioughby, Ontario,Canada, assignor to Norton Company, Worcester, Mass., a corporation ofMassachusetts Filed Feb. 25, 1958, Ser. No. 717,494 4 Claims. (Cl.23-208) The invention relates to the production of titanium carbide.

One object of the invention is to reduce the cost of synthesizingtitanium carbide. Another object of the invention is to provide apractical process for synthesizing titanium carbide from readilyavailable titaniferous ores such as rutile, and titania slag. Titaniaslag is a by-product resulting from the extraction of iron content fromcertain ilmenite ores, for example such as found in the Province ofQuebec.

Another object of the invention is to synthesize titanium carbideespecially suitable for the extraction of titanium metal by means of anelectrolytic process using a fused salt bath such as disclosed, forexample in a co-pending application of my colleagues Guy Ervin, Ira, andH. F. G. Ueltz, Serial No. 394,753, filed November 27, 1953, nowabandoned.

Another object of the invention is to provide a process of the typeindicated which will readily eliminate the silica content, the aluminacontent and iron content of the titaniferous ore as Well as othercompounds or elements occurring therein in minor percentages. Anotherobject of the invention is to produce high purity titanium carbide inparticle sizes suitable for the manufacture by sintering or the like ofcrucibles, cells or other bodies useful for the production of titaniummetal or otherwise in an arc furnace operation without the necessity offurther treatments such as Washing or crushing to fines. Another objectis to produce a titanium carbide suitable for the extraction of titaniummetal by various processes. Another object is to avoid contamination ofthe carbide product produced. Another object is to reduce the volume ofmolten carbide present at any given time in the furnace available forcontamination by air.

Another object is to produce titanium carbide having a content ofdesirable metal such as chromium, niobium, zirconium and/ or vanadiumfor the ultimate. production of titanium metal alloyed with such metalor metals.

This application is a continuation in part of by copending applicationSerial No. 455,920, filed September 14, 1954, now abandoned.

Other objects will be in part obvious or in part pointed outhereinafter.

In the accompanying drawings illustrating one type of arc furnace bymeans of which the process of the invention can be carried out,

FIGURE 1 is a front elevation of the furnace shell,

FIGURE 2 is a plan view of the furnace shell,

FIGURE 3 is a sectional view of the furnace shell, the section beingtaken along the line 33 of'FIGURE 1,

FIGURE 4 is a sectional view of the wall of the furnace shell, thesection being taken along the line 4-4 of FIG- URE 2,

FIGURES 5 and 6 are fragmentary sectional views taken on the lines 55and 6-6 respectively of FIG- URE 1, v,

FIGURES 7 and 8 are plan views of water-cooling r p Y FIGURE 9 is afront elevation of a furnace bottom truck,

3,161,472 Patented Dec. 15, 1964 FIGURE 10 is a plan view of the furnacebottom 1 truck,

FIGURE 11 is a sectional view taken along the line 11-41 of FIGURE 9,

FIGURE 12 is a front elevation of the furnace completely assembled,illustrating the carbon or graphite electrodes and the track upon whichthe wheels of the truck rest,

FIGURE 13 is a graph showing the operating conditions for the furnacedescribed,

FIGURE 14 is a diagrammatic elevational view of the arc furnace inoperation producing separate ingots of carbide material under eachelectrode.

Referring now to FIGURES 1, 2, and 3, the furnace shell 2t) can be madeout of two pieces of steel plate welded together. Its shape is oval,tapering from the bottom to the top, and the shape is sufficientlyindicated in FIGURES l, 2 and 3. As shown in FIGURES l, 4 and 5 at thetop of the shell 20 is Welded a lip 21 to which is welded a dependingskirt 22. At the bottom of the shell 20 is a large flange 23, which alsocan be made of steel plate and welded to this flange 23 is a dependingskirt 24. As clearly shown in FIGURE 3 the outer contour of the flange23 is circular while the inner contour is oval; the flange 23 is weldedto the shell 20. Steel ribs 25, 26, 27, and 28 are welded to the shell20 and to the flange 24 and serve to give this unit great strength.

Hooks 30 made of steel plate are welded to the outside of the shell 20,near the top, at opposite ends of the long axis of the oval. These hooks30 can be engaged by the hooks of chain falls connected to an overheadhoist, not shown, for the purpose of lifting the unit comprising theshell off the product of the fusion when the latter has cooledsufiiciently.

A pair of bent pipes 32, one of which is shown in FIGURE 7 and the otherof which is identical therewith except that it is of the opposite hand,are provided with very fine holes 33 which are preferably located (whenthe pipes 32 are in place as shown in FIGURES 4 and 5) to throw waterupwardly and inwardly; for example they can be 30 from the top and onthe inside as illustrated. At one end of each pipe 32 is a pair ofelbows 34 and 35 connected to each other and to a nipple 36. At theother end of each pipe 32 is a cap 3'7 to plug the free end of the pipewhereby to compel the water to issue through the holes 33. The pipes 32can be supported under the lip 21 in any manner; as illustrated inFIGURES 2 and 5 it will sufiice to provide four bolts 40 extendingthrough the lip 21 upholding bars 41 by means of nuts 42, and the pipes32 simply rest upon the bars 41.

FIGURE 8 illustrates one of a pair of bent pipes 45, of which one is asshown and the other is of the opposite hand, and these pipes 45 haveholes 46 and are equipped with'elbows 47 and 48 and a connecting nipple49 on one end, and caps 50 on the other end. As shown in FIGURES 1 and 6these .pipes can be supported close to the shell 20 by means of lugs 52welded to the outside of the shell 20 together with bent bolts 53passing through pipe sleeves 54 welded to the lugs 52, and with'nuts 55to draw the bent bolts firmly against the pipes 45. Illus trativcly theholes 46 can be oriented as shown in FiG- URE 6, but this is notcritical so long as they are located to throw the water inwardly sinceat the locus of pipe 45 there is already a cascade of water.

The pipes 32 and 45 are, of course, connected towater supply as by meansof hoses'57, 58, 59, and illustrated in FIGURE 12, so that at all timeswhen the power is on, the shell 20 is cooled by a cascade of water.Although the synthesis of titanium carbide takes place at about 3000 C.and above and steel plate melts at around 1500 C., the cascade of waterover the shell 20 coupled with the fact that steel is highly thermallyconductive protects the shell 20 from melting. The cascade of water hugsthe surface of the shell 20 and covers all parts of it from the top downand is assisted in so doing by the taper of the shell. Also it may beremarked that the shell 20 quickly acquires a coating of rust, which iseasily understood since it is alternately wet and dry and frequentlyquite hot, and the rust makes it much more wettable than clean, unrustedsteel.

Referring now to FIGURES 9 and 10, the furnace bottom truck comprises acircular table as made of steel plate to which is welded a dependingskirt 65 also made of steel plate. To the upper surface of table 65 iswelded an oval bottom container 67 made of steel plate. This oval bottomcontainer 67 has the same shape as the bottom of the shell 20 as shownin FIGURE 3, but the oval container 67 is slightly smaller in size sothat t e shell 20 and flange 23 can be placed over the container 67 andon the table 65. As shown in FIGURE 12, when the shell 20 is placed onthe bottom with the flange 23 on the table 65, a hose 69 is interposedto act as a seal. This hose 69 is a plain piece of rubber hose withoutcouplings or other fittings and simply acts as a cushion and sealingmeans,

and extends all the way around the table 65 with the ends thereofoverlapping.

Referring now to FIGURES 9 and 11 a pair of parallel steel I beams 7 arewelded to the bottom of the table 65 and a plurality of I beams 73, forexample three of them, are also Welded to the bottom of the table 65.These I beams 71 are desirably perpendicular to the I beams 70. To theouter I beams 71 are welded U-shaped bars '72, for the purpose ofconnecting a hook of a chain to the truck to draw it along the track 73illustrated in FIG- URE 12. V

Resting upon the track 73 are four flanged wheels 75 on steel axles 76journalled in bearing boxes 77 which can be iron castings. The wheels 75are located between the bearing boxes 77 and collars '73 on the axles76. The bearing boxes 77 are Welded to the under sides of the steel Ibeams 76.

Practical dimensions for the furnace described are, height of shell 2%about nine feet, other dimensions in proportion, and such a furnace canhold about 14,000 pounds of mixture and titanium carbide made therefrom.

A typical analysis of rutile ore, which is titaniferous ore, is given inthe following table.

1 By difference.

A. typicaltitania slag from the Qu bec Iron and Titanium Corporation ofSorel, Province of Quebec, analyzed as follows.

:3. TABLE ll Compound or element: Percentage of weight Ti0 77.27 A1 06.72 MgO 5.84 SiO 5.00 CaO 0.24- lron content, magnetic 4.24

This analysis shows no ZrO which was probably presem but undetermined.

I use for a charge in the electric arc furnacing operation a mixture ofthe titaniferous ore, coke and reclaim material from a previousfurnacing operation if I have any on hand that I consider ofsufficiently high grade. In a furnacing operation according to theinvention there is much material which is not converted to titaniumcarbide or is only partially converted and this is what I call reclaimmaterial. The unconverted material is called sweepings as it falls tothe floor when the furnace shell 20 is removed and the partly convertedmaterial which is found sintered around the outside of the pig is calledrefuse. Titaniferous ore and the two reclaim materials are genericallyreferred to as titanium oxide ore.

I provide such a quantity of coke that the free carbon content thereofwill be sufficient completely to reduce the titanium oxide ore and tocarbonize it to titanium carbide, TiC, and up to 100% excess freecarbon, that is to say from the stoichiometric proportion for suchcomplete reduction and carbonization up to double such stoichiometricproportion. Thus I calculate the mass of the ore on hand including thereclaim material, and by atomic Weights calculate the amount of carbonrequired to reduce and to carbonize the ore, then use thisstoichiometric amount or additional carbon up to double thestoichiometric proportion. Gf course the free carbon content of the cokeis figured to find out the actual amount of coke to add. Free carboncontent of coke determination is well known in the art and is done byanalytical methods.

The theoretical amount of free carbon required to reduce TiO to TiC is45% of the mass of the Ti0 one third or 33.3% excess of carbon is 60% ofthe mass of the TiO two thirds or 66.67% excess is 75% of the mass ofthe TiO and 100% excess of carbon is 0f the mass of the TiO I prefer touse a well calcined coke principally because the amount of free carbontherein can be determined with more accuracy. I can use various kinds ofcoke, petroleum coke, metallurgical coke and pitch coke, but in generalI find pitch coke is more uniform in quality and this usually has about90% free carbon and is low in ash content, below 1%. I prefer to selectcoke having less than 5% ash content.

The titaniferous ore is intimately mixed with the coke and is furtherintimately mixed with the reclaim material. I can use coarse ore and/ orcoke or fine ore and/ or coke, but the finer the particle sizes, thequicker and more complete is the reaction. The sweepings are used asthey come, being fine material. The refuse is crushed to particlesusually not larger than A inch lumps. The coke can be used as it comes,which is from /2 inch lumps to very fine particles. I can use reclaimmaterial (apart from the colre) or any proportion thereof relative tothe total titaniferous material.

Before assembling the shell 20 and the bottom container. 67, I form acarbon bottom in the container 67 in any suitable manner, such as bytamping in a mixture of fine carbon and pitch. This carbon bottom shouldbe concave on'the top andon the periphery should extend to the top ofthe container 67. After assembly of the shell 20 and bottom container67, I pack reclaim material and/ or ore between the outside of thecontainer'and the inside of the shell and then add more thereof to theshell 3 20 to extend to a rather uniform level about four inches abovethe top of the container 67 (assuming a nine foot high shell 20). Thisis also a bottom.

I now place a mass (for example about 75 pounds) of lump graphite orcarbon right under the eventual loci of the electrodes 80 (see FIGURE12) in which, when the furnace has been moved to operating position, arethe foci of the oval of the shell 20. Electrically connecting thesemasses of carbon or graphite (termed carbon) I build a bridge ofgraphite or carbon with this lump material which bridge extends from onelocus to the other locus. I form a trough in the reclaim material and/or ore for the lumps.

The bridge of graphite lumps forms a continuous electric current pathfrom the area under one electrode to the area under the other electrodeand the cross section of this path is preferably about fifty squareinches for the large furnace described. Maximum and minimum permissiblecross section of the bridge will be discussed hereinafter. I energizethe electrodes 80 at an E.M.F. of from 50 to 150 volts, preferably 100volts and then, having moved the truck on the track 73 to place theshell 20 in the proper position as above defined, I lower the electrodesinto contact with the graphite. During the entire process the electriccurrent flows through the bridge.

The electrodes are controlled by the usual overloadunderload servocontrolling mechanism and electric motor powered lifting and loweringmechanism, together with a circuit breaker to protect the electricalequipment. Since such electrical mechanisms are known and belong to anart other than the art of producing titanium carbide, they will not bedescribed herein.

When the electrodes 8!} contact the bridge of graphite, electric currentflows at about 4000 amperes or more. The servo mechanism causes theelectrodes 80 to hunt up and down maintaining the arcs with a currentflow (when the is 100 volts) of about 8000 amperes.

Now I shovel mixture all over the area of the furnace to a depth ofabout two inches. Some mixture gets right into the loci of theatres andthere the reaction takes place, forming titanium carbide and releasingcarbon monoxide. The conditions are reducing and the blanket of mixkeeps the air away from the zone of reaction in the loci of the arcs.While it is preferable to have the blanket of mixture about one inchminimum depth at the electrodes and measuring from the bottoms of theelectrodes in some cases I can operate without any blanket at all. Anyblanket of mix should not be more than about three inches as I want thegases to escape.

It now suffices to charge the furnace from time to time with mixture.Away from the electrodes the mix should be banked high all around theinside of the shell 20. For example, it may be four inches higher at theshell than at the electrodes, and even higher, up to a foot higher atthe ends of the long horizontal axis of the shell 2%.

As mixture is fed from time to time into the furnace, the electrodesgradually rise as ingots of titanium carbide are formed in the loci ofthe arcs. No considerable pool of molten titanium carbide is formed; thereaction produces a titanium carbide which is incandescent and someliquid phase may exist but for the most part the liquid phase ismomentary only.

The operation of the furnace part way through a run as described aboveis illustrated in FIG. 14, which shows the base layer 82 of ore, reclaimmaterial or comparable material supporting the large lumps 84 and 84a ofgraphite or carbon under the loci of the electrodes 80. Between thecarbon lumps 84 and 84a is the bridge of graphite or carbon lumps 86 andextending substantially between the bottom of each electrode 89 and thecorresponding large carbon lump 84 or 84a are the fused ingots 88 and88a of carbide material. Surrounding the bottom ends 6f the electrodes80, ingots 88 and 88a and carbon bridge formed of lumps 84, 84a and 86is the mass of reaction mixture 9%, which as exampled above will risehigher and higher in the shell 20 as the production run proceeds. Thepath of electric current during the operation is from one electrode viaan arc 92, through the ingot 88, the lump 84, then the lumps 86, nextthe lump 84a, then the ingot 88a, and finally through the arc 92a to theother electrode.

When the run has been completed, and the electrodes lifted, it isconvenient to draw the truck along the rails 73 to remove the entirefurnace from under the electrodes so that, for example, another similarfurnace may be set up underneath them to start another run of theprocess. However, for a long time the cascade of water is maintained onthe shell 20, preferably at least through the hoses 57 and 58 to thepipes 32. This cascade of water is maintained until the contents of theshell 20 has cooled sufliciently so that there is no more danger ofburning the shell. Usually this takes about sixteen hours. The furnaceshell is not lifted until the contents have cooled sufficiently so thatthe carbide will not oxidize when it comes into contact with the air. Ina 14,000 lb. furnace shell this is about 40 hours from the time thefurnace is shut down. At the end of that time, the furnace shell islifted off the ingots and what is now reclaim material, which forms aloosely sintered mass. Two ingots of titanium carbide are found embeddedin the mix. The ingots are carefully separated from What is nowreclaimed material and the latter is collected for use in a subsequentrun of the process.

EXAMPLE I Using a furnace the shell 2% of which was 38 inches highinstead of the furnace recommended, which 38 inch high shell will hold amaximum of about 1000 lbs. of this material, this one thousand poundfurnace being, however, of the same shape and proportions and having thesame parts as the fourteen thousand pound furnace described, Isynthesized thirty-six pounds of titanium carbide as follows:

The charge was 300 pounds of rutile and 200 pounds of pitch coke havinga free carbon content of Thus the coke had one hundred eighty pounds offree carbon which is 60% of the mass of the rutile which was so nearlypure TiO that I disregarded the difference. The

actual analysis of this rutile was as follows.

Table III Compound: Percentage by weight Ti0 94.8 Fe O 1.15 Undetermined4.05

The 4.05% undetermined can be the oxides of Table I in said table.

The rutile was a fine material the largest particles of which were ofabout 46 grit size, the remainder finer particles all the way down toparticles of a few microns size. The coke was fairly uniform in particlesize being about the same size as grains of rice. The rutile and thecoke were well mixed.

My assistants under my direction then prepared the furnace bottom asalready described by charging it with rutile and then laid down thegraphite masses and built the graphite bridge which were four incheswide and about two inches deep. The two graphite electrodes were fourinches in diameter.

The furnace was started under an electromotive force of 50 volts with apower input of kw. giving an average of 3000 amperes. The furnace wasfed as described until all of the five hundred pounds of charge (mix)had been fed thereinto. I kept the blanket or cover of mix at about oneinch. Of course this is an estimate since the contents of the shellemits tremendous illumination assumed to have been in about the sameproportions as at the temperatures involved. This run took four hoursand seventeen minutes.

The yield was thirty six pounds of titanium carbide having an analysisas follows.

Of the 7.05% not accounted for, obviously with so little boron to beginwith, there could be very little in the product. Also the temperature isabove the decomposition point of boron carbide and above the boilingpoint of B There can be little nickel in the product for similarreasons. The silicon, aluminum, calcium and magnesium are largelyeliminated since the temperature is above the boiling points of theseelements and above the decomposition points of silicon carbide andaluminum carbide. I believe the calcium and magnesium were largelyeliminated. The phosphorus, tin and sulphur content is certainly mostlyeliminated because of their low boiling points and the instability oftheir compounds. This leaves the elements Cr, Nb, V, and Zr as well asthe Ti, C and Fe. The charge probably picked up a smfll percentage ofnitrogen. Also some oXy en probably was present in the 7.05 percentremainder.

The ingots, one under each graphite electrode, were roughly cylinderswith cracks. Each ingot was broken up with sledges and then crushed toproduce lumps of various sizes, many an inch or two in longestdimension. Whatever is done with this material after this point is nopart of the present invention. The material, however, is well suited forthe uses mentioned in the objects.

This run, besides producingthirty-six pounds of titanium carbide yielded85 lbs. of sweepings and 107 lbs. of refuse making 192 lbs. of reclaimmaterial useful for further production of TiC. Some of the titaniumcontent was lost in dust. In a large scale operation a dust collector isused to recover most of the dust.

EXAMPLE H In this example the mass of the charge, the electromo- Table VElement: Percentage by weight Ti 71.47 c 24.10 Fe 0.31

The balance of 4.12% probably involved the elements mentioned in thediscussion of Table 1V. Quantitatively there was probably considerablyless oxygen in the material of Example H than there was in the materialof Table IV (Example I). The ingots were broken up and crushed as in thecase of Example I. This TiC was better grade material: than that ofTable IV for the uses mentioned in the objects since more of the oxygenwas eliminated. The percentage of Ti in TiC is 80 and the percentage ofcarbon therein is therefore 20. It is noted that for the purposesindicated in the objects excess of carbon is not detrimental since, inthe production of titanium metal by electrolysis in a fused salt' baththe carbon will not deposit on the cathode.

In this run the sweepings weighed 67 lbs, the refuse weighed 104 lbs.making a total of 171 lbs. of reclaim material for subsequent use.

EXAMPLE III Table VI Element: Percentage by weight Ti 69.37 C 27.19 Fe0.14

This product had less oxygen than those of Example I and ii becausethere was 96.56% total titanium and carbon as compared with 95.57% forExample ll, Table V and 92.64% for Exarn le I, Table IV. Probably thisproduct contained elements such as Cr, Nb, V and Zr in about the samerelative proportions undetermined as in the cases of Examples 1 and H.The ingots were broken up crushed as in the case of the other examplesproviding the best grade material for the uses mentioned. In this runthe sweepings weighed 72 lbs, the refuse weighed lbs, making a total of162 lbs. of reclaim material for subsequent use.

EXAMPLE TV I have also made a run using an amount of coke to yield freecarbon which was only the theoretical amount required to reduce thetitania to titanium carbide, to wit, .45 times the amount of TiO whichagain I took to be the total mass of the rutile. The samerutile (TableIll) was used and the same pitch coke having 88.7% free carbon. The massof the charge, the electromotive force, the power in kilowatts and themanner of feeding the furnace were all of them the same as in thepreceding examples. The charge was 335 lbs. of rutiie and lbs. of coke.This run took three hours and five minutes. The yield was 23 lbs. oftitanium carbide analyzing:

This material is also believed to be useful for the extraction oftitanium metal for example by chlorination. There is in the material ofExample 1V some suboxides of titanium, such as TiO and TlgG. Thereaction of chlorine with TiC is exothermic while the reaction of theoxides of titanium with chlorine is endothermic. By using this materialcontaining the carbide and some oxides of titanium the reaction withchlorine to produce titanium tetrachloride TiCL; can be more closelycontrolled. The process for the extraction of titanium from itstetrachloride is lmown. V

This material is further calculated to consist of:

--the bridge is the criterion,

One of the especial features of the present process is having anelectrically conductive path for the current between the arcs consistingof two ingots of titanium carbide separately formed under the electrodesplus the graphite bridge underneath the ingots. When finally the furnacehas been filled with mixture to the brim, the power is out oh and theelectrodes are raised. Of course the cascade of water was flowing overthe furnace shell 20 at all times during the run of the process.

Another feature of the invention is the layer of rutile or reclaimmaterial below the graphite or carbon bridge. This serves as aninsulating layer to prevent short circuiting of the electric currentpath.

With regard to the electrical parameters, I have not found it practicalto use higher than 150 volts and under 50 volts it is difficult to makea satisfactory product in reasonable quantity.

The important parameters in this invention are the parameters of theelectromotive force, the proportion of free carbon in the mix and theparameters of the bridge. With regard to the latter, the cross sectionof since the bridge length is simply determined by the fact that itextends from under one electrode to under the other electrode, referredto as the loci of the electrodes.

The important feature of the cross section of the bridge is its areasince the shape can vary widely within reason. This area is given as afunction of the electrode diameter as I know of no other practical wayto state it. The electrode diameter can be almost anything dependingupon the size of the furnace. If the electrode is square, triangular orsome other shape in cross section its diameter is taken as a function ofits area A as if it were a circle. The diameter D of any circle is equalto 7| and for any figure the effective diameter D can be found by theequation Brit/Z 7r In the practice of my invention I prefer to use theoval shell and two electrodes with single phase power. However threephase power could be used with three electrodes and then the shellshould be trilobed or round.

The are furnace process described, synthesizing titanium carbide,consumes far less pounds of electrode for every pound of production thandoes the resistance furnace process of the patent to Ridgway, No.2,237,503. I do not have exact figures but am confident that theelectrode consumption of my arc furnace process is less than one-tenthof that of the resistance furnace process per unit of product. Also myarc furnace process uses substantially less power per unit of productionthan does the resistance furnace process of Patent No. 2,237,503.Furthermore the production rate of my arc furnace process is muchgreater than that of the resistance furnace process.

The furnace shell 20, the table 65 and the oval bottom container 67 arestated to be made of steel. Steel is a variety of iron and othervarieties of iron could be used, and also other metals could besubstituted. Mixtures of two or more of the refractory materialsalumina, titania and zirconia could be used for the furnace bottom underthe carbonaceous bridge. The electrodes used were cylindrical in shape,but rod like electrodes of non- 10 circular cross section could be used.The ends of the graphite bridge covered the entire areas under the areasof the electrodes and this is preferable.

The process of the invention described herein is surprising when it isconsidered that the melting point of titanium carbide is 3140 C. whilethe boiling point of titanium metal is 3000 C. As there is no lid on thefurnace one could expect the material to boil off when it has beenreduced to the elemental stage. For it is obvious that you cannot gofrom TiO to TiC without passing through the stage Ti. As a matter offact there are many stages or steps in the process going down (reducing)from Ti0 to TiC. We have:

TABLE IX Name Formula Titanium Dioxide Titanium Sesquioxide TitaniumMonoxide-.. Titanium Suboxide Dititanium Oxide Titanium Titanium OarbidFigures are degrees centigrade, B.P.=boiling point.

When TiO decomposes it goes to a lower oxide and the same is true for TiO I believe the lower oxides do not decompose to still lower oxides orto the metal because if so I would not need to add so much carbon. One,two or all of TiO, Ti O and Ti O have a boiling point well below 3000C., as calculated by thermodynamics, so it is surprising that TiC can besynthesized in the manner described.

By free carbon I mean available carbon, that is carbon available forreduction as distinguished from carbon in the hydrocarbon content, etc.;sometimes free carbon is called fixed carbon. Since graphite is a formof carbon and since amorphous carbon can be used for the bridge as wellas graphite, in the claims the expression bridge of carbon or the likeis to be construed as covering a bridge of graphite or a bridge ofamorphous carbon.

In the patent to R. R. Ridgway, No. 2,285,837, a process of producingcarbides, including titanium carbide, in an arc furnace is described. Inthis Ridgway process a molten pool of the carbide is formed, as shown inthe drawings and as stated on page 3, left hand column, line 9. This wasfound to cause reoxidization of the carbide resulting in a low gradeproduct. The theory that the use of a deep furnace would avoidoxidization and nitriding was valid only in part. By avoiding theformation of any substantial pool of molten carbide, the process hereindescribed is a much more practical arc furnace method of making titaniumcarbide and produces a better product.

Further details of the operating conditions for a furnace of the sizeillustrated and described which also hold for furnaces of about the samesize with electrodes approximately as described are as follows:

The first adjustment to be made when the furnace is ready to start is toset the voltage at a suitable value. The range of voltages that can beused with the furnace noted above is from 50 to 150 volts; therecommended value for best operation being volts. The adjustment is thecurrent level. The current controller raises or lowers the electrodesautomatically to maintain a predetermined current. The range of currentsthat can be used is from 4,000 to 10,000 amperes, the optimum valuebeing 8,000 amperes. Under optimum conditions, this size and type offurnace therefore runs at 100 volts and 8,000 amperes, corresponding toa total input of 800 kva. This type of furnace runs at a power factorsufficiently close to unity for us to speak of kva. and kw.interchangeably, so I shall call this 800 kw.

The ranges of voltage and current noted above still do not specifycompletely the possible operating conditions.

For example 150 volts at 10,090 amperes would cause erratic furnaceoperation while 50 volts and 4,000 mm peres would reduce the rate ofproduction to an uneconomically low level. A further limitation musttherefore be placed on the operation, restricting the power level to therange from 350 to 1000 kw. FIGURE 13 shows graphically the permissibleoperating conditions.

The discussion above describes a comparatively wide range of powerlevels, roughly three to one. It is to be expected that the resultingproduct will differ in some respects, depending on the particular set ofoperating conditions selected, and this expectation is borne out byexperience. For one thing, the power level will determine the diameterof the twin ingots that grow in the furnace. Thus, at the lower limit of350 kw. the ingots will be about 14 inches in diameter, and at the upperlimit of 1000 kw. they can be up to 24 inches in diameter. Since theelectrodes are spaced 24 inches center to center, the latter figuresrepresent a limiting condition under which the ingots begin to toucheach other at some points. For-another thing, the power level willinliuence the rate at which the ingots grow vertically. However, thisrate of growth is taken care of automatically providing the rawmaterials are fed to the furnace at the specified rate, which I shallnow discuss.

Probably the most important single consideration in the operation of thefurnace is the control of the process of reaction and incipient fusionthat makes it possible to grow ingots without at any time forming amolten pool of product in the bottom of the furnace. This process iscontrolled by feeding the raw materials to the furnace at apredetermined rate. Thus the feed rate must be held between 0.5 and 0.75lb. of raw mix per kWh. As an example, if the furnace is run at a powerlevel of 1,000 kw., the total energy used in one hour is 1000 kwh. Itwill therefore be necessary to feed the raw mix to the furnace at a ratebetween 500 and 750 lb. per hour.

Since by no means all the feed is reacted in any one run, the overallconsumption of electrical energy by the process is 48 kwh. per lb. ofproduct.

It will thus be seen that there are as many distinct ingots of titaniumcarbide as there are electrodes, and that the ingots are maintainedsubstantially clear of each other so that the major path of the electriccurrent after the process has been started is from one electrode toanother electrode, via first an electric are between an electrode andthe titanium carbide ingot under it, then through a mass of carbon, thenthrough the bridge, then through another carbon mass, then throughanother titanium carbide ingot and finally through an electric arc tothe electrode directly above the ingot.

It will thus be seen that there has been provided by this invention aprocess for the production of titanium carbide in which the variousobjects hcreinbefore set forth, together with many thoroughly practicaladvantages are successfully achieved. As many possible emsediments maybe made or the above invention and as the art herein described might bevaried parts, all without departing from the scope of the invention, itis to be understood that all matter hereinabove set forth or shown inthe accompanying drawings is to be interpreted as illustrative and notin a limiting sense.

I claim:

1. The process of synthesizing titanium carbide by the reaction oftitanium oxide ore and coke in an electric arc furnace while maintainingreducing conditions at the zones of reaction, which comprises forming inan electric arc furnace having vertically movable electrodes a furnacebottom of refractory oxide material, placing a mass of carbon above saidbottom at the eventual locus of each electrode, forming a bridge ofcarbon above said bottom electrically connecting said masses,maintaining said bridge of carbon at all times during the process,placing said electrodes at said loci in electrical contact with saidmasses of carbon and energizing said electrodes at from 5 0 to volts,maintaining during the process a mixture of said titanium oxide ore andcoke around the bottoms of said electrodes and forming thereby as manydistinct ingots or" titanium carbide as there are electrodes one ingotunder each electrode, feeding said mixture of titanium oxide and coke toaround the bottoms of said electrodes at the rate of from 0.5 to 0.75lb. of mixture per kwi. or" electrical energy energizing saidelectrodes, and maintaining the said ingots clear of each other wherebythe path of the electric current after the process has been started isalways from one electrode to another electrode, via first an are, thenthrough a titanium carbide ingot synthesized by the process, thenthrough one of said masses of carbon, then through the bridge, thenthrough another of said masses of carbon, then through another titaniumcarbide ingot synthesized by the process, then by an arc to anotherelectrode, and building up the titanium carbide ingots synthesized bythe process under the electrodes without the formation of anyconsiderable pool of molten titanium carbide as the electrodes graduallyrise during the process by reason of the energization of the electrodesat 1 kwi. for each 0.5 to 0.75 lb. of mixture fed.

2. lrocess according to claim 1 in which the cross section of the bridgein square inches divided by the diameter of the electrode in inches isbetween 2 and 12.

3. Process according to claim 2 in which the oxide material of thefurnace bottom is mainly titanium oxide.

4. Process according to claim 1 in which the oxide material of thefurnace bottom is mainly titanium oxide.

References Qited by the Examiner UNETED STATES PATENTS 2,237,503 4/41Ridgway 23-208 2,285,837 6/42 Ridgway 23208 MAURICE A. BRINDISI, PrimaryExaminer.

1. THE PROCESS OF SYNTHESIZING TITANIUM CARBIDE BY THE REACTION OFTITANIUM OXIDE ORE AND COKE IN AN ELECTRIC ARC FURNACE WHILE MAINTAININGREDUCING CONDITIONS AT THE ZONES OF REACTION, WHICH COMPRISES FORMING INAN ELECTRIC ARE FURNACE HAVING VERTICALLY MOVABLE ELECTRODES A FURNACEBOTTOM OF REFRACTORY OXIDE MATERIAL, PLACING A MASS OF CARBON ABOVE SAIDBOTTOM AT THE EVENTUAL LOCUS OF EACH ELECTRODE, FORMING A BRIDGE OFCARBON ABOVE SAID BOTTOM ELECTRICALLY CONNECTING SAID MASSES,MAINTAINING SAID BRIDGE OF CARBON AT ALL TIMES DURING THE PROCESS,PLACING SAID ELECTRODES AT SAID LOCI IN ELECTRICAL CONTACT WITH SAIDMASSES OF CARBON AND ENERGIZING SAID ELECTRODES AT FROM 50 TO 150 VOLTS,MAINTAINING DURING THE PROCESS A MIXTURE OF SAID TITANIUM OXIDE ORE ANDCOKE AROUN THE BOTTOMS OF SAID ELECTRODES AND FORMING THEREBY AS MANYDISTINCT INGOTS OF TITANIUM CARBIDE AS THERE ARE ELECTRODES ONE INGOTUNDER EACH ELECTRODE, FEEDING SAID MIXTURE OF TITANIUM OXIDE AND COKE TOAROUND THE BOTTOMS OF SAID ELECTRODES AT THE RATE OF FROM 0.5 TO 0.75LB. OF MIXTURE PER KWI. OF ELECTRICAL ENERGY ENERGIZING SAID ELECTRODES,AND MAINTAINING THE SAID INGOTS CLEAR OF EACH OTHER WHEREBY THE PATH OFTHE ELECTRIC CURRENT AFTER THE PROCESS HAS BEEN STARTED IS ALWAYS FROMONE ELECTRODE TO ANOTHER ELECTRODE, VIA FIRST AN ARC, THEN THROUGH ATITANIUM CARBIDE INGOT SYNTHESIZED BY THE PROCESS, THEN THROUGH ONE OFSAID MASSES OF CARBON, THEN THROUGH THE BRIDGE, THEN THROUGH ANOTHER OFSAID MASSES OF CARBON, THEN THROUGH ANOTHER TITANIUM CARBIDE INGOTSYNTHESIZED BY THE PROCESS, THEN BY AN ARC TO ANOTHER ELECTRODE, ANDBUILDING UP THE TITANIUM CARBIDE INGOTS SYNTHESIZED BY THE PROCESS UNDERTHE ELECTRODES WITHOUT THE FORMATION OF ANY CONSIDERABLE POOL OF MOLTENTITANIUM CARBIDE AS THE ELECTRODES GRADUALLY RISE DURING THE PROCESS BYREASON OF THE ENERGIZATION OF THE ELECTRRODES AT 1 KWI. FOR EACH 0.5 TO0.75 LB. OF MIXTURE FED.